Sea-level rise from land subsidence in major coastal cities

Abstract

Coastal land is being lost worldwide at an alarming rate due to relative sea-level rise (RSLR) resulting from vertical land motion (VLM). This problem is understudied at a global scale, due to high spatial variability and difficulties reconciling VLM between regions. Here we provide self-consistent, high spatial resolution VLM observations derived from Interferometric Synthetic Aperture Radar for the 51 largest coastal cities, representing 22% of the global urban population. We show that peak subsidence rates are faster than current global mean sea-level rise rates and VLM contributions to RSLR are greater than IPCC projections in 90% and 53% of the cities respectively. Localized VLM worsens RSLR impacts on land and population in 73-75% of the cities, with Chittagong (Bangladesh), Yangon (Myanmar) and Jakarta (Indonesia) at greatest risk. With this dataset, accurate projections and comparisons of RSLR effects accounting for VLM are now possible for urban areas at a global scale. Sea-level rise resulting from climate change has rightly received substantial attention from researchers, practitioners and the public as an ongoing threat that needs to be addressed 1 . Yet lesser attention has been paid to land subsidence which can exceed tens of mm/year 2-4 , and increase local relative sea-level rise (RSLR) many times that of global mean sea-level rise of few mm/year alone 5,6 . Local RSLR, defined as sea-level rise relative to local land height, is what effectively matters for any coastal community. Furthermore, many coastal areas experiencing the fastest land subsidence are major cities built on flat, low elevation river deltas, exposing large populations and substantial economic value to the impacts of local RSLR 7,8 . Consequently, it is crucial to consider land subsidence when assessing coastal risks of RSLR 9,10 . Vertical land motion (VLM) -either subsidence (downward land motion) or uplift (upward land motion) -can be caused by several factors such as tectonics 11,12 , natural compaction of sediments 7,8 , groundwater, oil, and gas extraction 2,4 , reduced aggradation due to dams, levees, and loss of coastal vegetation 5 , and glacial isostatic adjustment 13,14 . Because these contributing factors vary significantly over a range of temporal and spatial scales, the contribution of VLM to RSLR has been difficult to assess on a global scale 15 . Many local-to regional-scale studies have mapped VLM at different coastal localities over different time

WITHDRAWN: The contribution of diminishing river sand loads to beach erosion worldwide

“…With a ~ 20 cm rise in the sea level since 1900 (Oppenheimer et al 2019), the sea has gained up to 15 metres on land for beaches with a slope of 1 degree. Local subsidence due to sediment compaction following freshwater pumping can reach several metres as in Japan or Indonesia (Cao et al, 2021;Tay et al, 2022), greatly exceeding any other cause for coastline evolution. Abrupt, or progressive or transient vertical uplift or subsidence on the scale of centimetres to metres over a period of years can locally influence the relative sea-level rise substantially (e.g., Jeanson et al, 2021), and consequently the coastline position (Farías et al, 2010).…”

Vertical land motion reconstruction unveils non-linear effects on relative sea level

“…Therefore, future efforts could further advance our presented model by incorporating discontinuous effects, e.g., by probabilistically simulating VLM responses to earthquakes Vertical land motion reconstruction unveils non-linear effects on relative sea level cha in regions of high tectonic activity (see, e.g., [49]). Other remaining challenges are the lack of human-induced VLM projections [47] and low station coverage, in particular in highly populated regions, which are especially vulnerable due to high subsidence rates [41,64]. Therefore, recent studies have developed VLM projections linked to different groundwater-extraction scenarios [65], and increasingly expanded VLM observations in space using InSAR to enable local sea level projections at an unprecedented resolution [34,64,66].…”

Evaluating Knowledge Gaps in Sea‐Level Rise Assessments From the United States

“…For example, assessed projections in the Mississippi Delta region in the U.S. (a region dealing with substantial subsidence; Abadie et al, 2020;G. G. Garner et al, 2021) as well as assessed projections along the U.S. Southeast coast (where ocean dynamic effects and gravitational and rotational deformation effects from the Greenland Ice Sheet contribute to accelerated SLR; G. G. Garner et al, 2021) , 2017;Shirzaei et al, 2020;Tay et al, 2022). Furthermore, local assessments are sparse along the Gulf coast and U.S. Southeast coast, with many projections in these regions coming from a report generated by the NPS (Caffrey et al, 2018).…”

“…of Land and Natural Resources, 2017). For example, the Louisiana Coastal Master Plan calculates subsidence rates, but provides this information as a separate risk factor from local SLR estimates, resulting in an assessed SLR value that does not fully capture relative SLR for a region that is greatly impacted by vertical subsidence (Coastal Protection and Restoration Authority, 2017; Shirzaei et al., 2020; Tay et al., 2022). Furthermore, local assessments are sparse along the Gulf coast and U.S. Southeast coast, with many projections in these regions coming from a report generated by the NPS (Caffrey et al., 2018).…”